Servomechanism

ABSTRACT

A SERVOMECHANISM IN WHICH A TORQUE MOTOR DRIVES A FLAPPER ARM. THE FLAPPER ARM CONTROLS POSITIONING OF A PAIR OF SPOOL MEMBERS. EACH OF THE SPOOL MEMBERS MOVES INSIDE A PORTED BUSHING. MOVEMENT OF EACH SPOOL CONTROLS PORTS WHICH CAN BE USED TO SUPPLY FLUID UNDER PRESSURE TO A HYDRAULIC MOTOR. THE HOUSING OF THE TORQUE MOTOR IS MOUNTED FOR SWINGING ABOUT A PAIR OF TRANSVERSELY EXTENDING AXES TO SET BOTH THE RELATIVE AXIAL POSITIONS OF THE SPOOL MEMBERS AND THEIR NULL POSITIONS RELATIVE TO THE PORTED BUSHINGS.

United States Patent [1 1 Taylor [451 Sept. 18,1973

1 1 SERVOMECHANISM [76] Inventor: William W. Taylor, Suite 103 5300 Hamilton Avenue, Cincinnati, Ohio [22] Filed:

June 1, 1971 I 21 Appl; No.: 148,695 7 Related U.S. Application Data [63-] Continuation-in-part-of Ser. No. 71,133, Sept. 10,

1970, abandoned.

[52] U.S. Cl 91/459, 91/465, 9l/469, 9l/49, 137/625.6l, 137/82 [-51] Int. CL. FlSb 13/044, Fl6k 11/07 [58] Field of Search 91/465, 469, 459,

[56] References Cited UNITED STATES PATENTS 2,832,318 4/1958 'Paine 137/82 3,055,383 9/1962 Paine 137/625.6l

3,598,151 8/1971 Shore 137/625.6l 2,771,061 [1956 Farron 91/465 2,880,708- 4/1959 llayner 91/465 FOREIGN PATENTS OR APPLICATIONS 976,800 1111950 France 91/465 Primary ExaminerPaul E. Maslousky Attorney-Pearce & Schaeperklaus [57] ABSTRACT A servomechanism in which a torque motor drives a flapper arm. The flapper arm controls positioning of a pair of spool members. Each of the spool members moves inside a ported bushing. Movement of each spool controls ports which can be used to supply fluid under'pressure to a hydraulic motor. The housing of the torque motor is mounted for swinging about a pair of transversely extending axes to set both the relative axial positions of the spool members and their null positions relative to the ported bushings.

16 Claims, 34 Drawing Figures PATENTEUSEPIBIQB 3.759.145

' SHEET 1 0f 8 WILLIAM w TAYLOR Attorneys PATENTED SEP 1 8 i973 SHEET 2 0F 8 FIG.7

FIG.4

FIG. .5

FIG. 9

FIG.8

INVENTOR. WILLIAM W. TAYLOR Attorneys PAIENIED EH 3.759.145

SHEET 3 0F 8 INVENTOR. WILLIAM W. TAYLOR Attorneys PATENTEI] SE?! 8 I975 SHEET [1F 8 INVENTOR. WILL 1AM W. TAY LOR www Attorneys PAIEmEusE 3.759.145

I SHEET 7 BF 8 FIG. 28

INVENTOR.

WILLIAM W. TAYLOR Z, K/JZMM SERVOMECIIANISM This is a continuation-in-part of my co-pending application Ser. No. 71,133 filed Sept. 10, 1970, now abandoned.

This invention relates to electrohydraulic servovalves, particularly to two-stage servovalves.

In Hydraulic Control Systems by Herbert E. Merritt published by John Wiley & Sons, Inc., illustrations appearing on pages 202 and 213 are typical of two-stage electro-hydraulic servovalves with which I was acquainted prior to making of the instant invention. Such valves as there illustrated present problems of very serious character in manufacture, as the spool and the bushing or body of such valves each has four radial metering surfaces and all eight thereof must be located with a great degree of accuracy, of the order of 0.000] inch. Manufacture of such valves commonly involves calibration in which fluid volumes passing through the valve are measured in relation to position of the valve spool relative to the surrounding bushing or body. The values obtained are analyzed, for example, graphically. The valve is then disassembled, parts thereof are further machined and calibrated as is indicated until the desired quality is obtained. The assembly, calibration, disassembly, remachining, cleaning, reassembling, recalibration type activity results in substantial increase in costs and in the valves produced the critical parts are not interchangeable.

An object of this invention is to provide a two-stage servovalve which may be manufactured at substantially reduced cost.

Another object of this invention is to provide a device of the above character in which calibration can be accomplished without disassembly of the valve.

Another object of this invention is to provide a valve in which a pair of spools is disposed in respective bushings, each of which has two radial metering surfaces precisely spaced in position and which spools are related to each other by hydraulic means cooperating with a flapper of an electric torque motor which shifts the flapper in response to electric control signals.

Briefly, this invention provides a servomechanism in which a motor is pivotally mounted and includes a housing swingably mounted on the swivel mount. A flapper arm is driven by the motor. A pair of valve spool members move transversely of the flapper arm. Flapper nozzles carried by the spools are directed toward the flapper arm. Fluid under pressure discharges through the flapper nozzles, and pressure inside each flapper nozzle is increased as the flapper arm approaches a flapper nozzle and is decreased as the flapper arm moves away therefrom. The pressure inside the flapper nozzles moves the spools to restore predetermined spacing between flapper nozzles and flapper arms, and movement of the spools operates ports to control a hydraulic actuator. Each spool controls ports which supply pressure and remove fluid for movement of the actuator in one direction. The spools move together without any mechanical link therebetween.

The above and other objects and features of the invention will in part be apparent and will in part be obvious to those having ordinary skill in the art to which this invention pertains from the following description and the accompanying drawings, in which like reference characters indicate like parts.

In the drawings:

FIG. 1 is a top plan view of a two-stage electrohydraulic servovalve with portions thereof broken away to illustrate details of construction and embodying the instant invention;

FIG. 2 is a view partly in side elevation of the valve of FIG. 1 and partly in section taken along the line 2-2 in FIG. 1, spool and bushing members being omitted for clarity;

FIG. 3 is a view in transverse section taken generally on the line 3-3 in FIG. 1;

FIG. 4 is a top plan view of the body of the valve of FIG. 1;

FIG. 5 is a view in side elevation of the body of the valve of FIG. 1;

FIG. 6 is a view in end elevation of the body of the valve of FIG. 1, transverse adjustment screws of the servovalve being shown in association therewith;

FIG. 7 is a view in horizontal section taken on the line 7-7 in FIG. 5;

FIG. 8 is a view in horizontal section taken on the line 8-8 in FIG. 5;

FIG. 9 is a view in section taken along the line 99 in FIG. 5;

FIG. 10 is an enlarged view in section showing details of construction of the valve of FIG. 1;

FIG. 11 is a top plan view of a valve spool of the servovalve shown in FIG. 1, guide pins thereof being omitted for clarity;

FIG. 12 is an end view of the valve spool of FIG. I 1;

FIG. 13 is a view in section taken on the line 13-13 in FIG. 12;

FIG. 14 is a schematic view in end elevation of the valve spool of FIG. 11 showing the passageways illustrated in FIG. 13;

FIG. 15 is a view in section taken on the line 15-15 in FIG. 12;

FIG. 16 is a schematic view in end elevation of the spool of FIG. 11 showing the passageways illustrated in FIG. 15;

FIG. 17 is a view partly in front elevation and partly in section of a bushing forming a part of the servovalve of FIG. 1;

FIG. 18 is a view in section taken on the line 18-18 in FIG. 17;

FIG. 19 is a view in enlarged section taken on the line 19-19 in FIG. 14;

FIG. 20 is a perspective view of a swivel member which forms a part of the servovalve of FIG. 1, transverse adjustment screws being shown in association therewith;

FIG. 21 is a view in upright section of a servovalve constructed in accordance with another embodiment of this invention, spool and bushing members being omitted for clarity;

FIG. 22 is a view in section taken generally on the line 22-22 in FIG. 21;

FIG. 23 is a view in side elevation of the body of the valve shown in FIGS. 21 and 22;

FIG. 24 is a view in end elevation of the body of the valve shown in FIGS. 21-23;

FIG. 25 is a view in horizontal section taken on the line 25-25 in FIG. 23;

FIG. 26 is a view in horizontal section taken on the line 26-26 in FIG. 23;

FIG. 27 is a view in horizontal section taken on the line 27-27 in FIG. 23;

FIG. 28 is an enlarged view in section showing details of construction of the valve shown in FIG. 21;

FIG. 29 is a view partly in side elevation and partly in section of a bushing forming a part of the servovalve of FIG. 21;

FIG. 30 is a view in section taken on the line 30-30 in FIG. 29;

FIG. 31 is a view in lengthwise section of a valve spool of the servovalve of FIG. 21, a dash-pot member and a fragmentary portion of a flapper shoe being shown in association therewith;

FIG. 32 is a view in section taken on the line 32-32 in FIG. 31;

FIG. 33 is a fragmentary view in section on an enlarged scale of a portion of the spool shown in FIG. 31 with fragmentary portions of the flapper and the dashpot member being shown in association therewith; and

FIG. 34 is a view in side elevation of a ring member forming a part of the servovalve of FIG. 21.

In the following detailed description and the drawings, like reference characters indicate like parts.

In FIGS. 1, 2 and 3 is illustrated a two-stage electrohydraulic servovalve 20 constructed in accordance with an embodiment of this invention. The servovalve 20 has a body 21 in the lower portion of which the hydraulic valve portions of the structure are located and in the upper portion of which is mounted an electric torque input motor 22 having a flapper 23 (FIGS. 2 and 3) which includes a flapper shoe 124 which hydromechanically cooperates (FIG. with valve spools 24, 25 reciprocably mounted in valve sleeves or bushings 26, 27 which are in turn respectively mounted in parallel bores 28, 29. As shown in FIG. 5, the valve body 21 is provided with a supply or inlet port 30 through which hydraulic fluid under pressure from a suitable source, not shown, may move into cavities provided in the valve body 21, and a return or outlet port 31 through which hydraulic fluid may be discharged or returned from the valve body, and two line ports 32, 33, sometimes hereinafter also respectively called Line 1 and Line 2, which, as shown schematically in FIG. 10, may be coupled to a hydraulic device to be operated in response to the servovalve such as a reciprocating ram type hydraulic output actuator or motor 34 through respective hydraulic lines 35, 36 to effect positioning of ram piston 34' in accordance with input signals communicated to the electrohydraulic servovalve.

As shown in FIG. 7, the valve body 21 is so bored that supply or inlet port 30 extends into a gallery bore 37 which in turn places bore 30 in communication with cross bores 38, 39. As shown in FIG. 7, a portion of bore 37 is filled by plug 37 and, in similar fashion plugs 38 and 39' respectively close portions of bores 38 and 39. Bore 38 communicates with the passages 40, 41 (FIG. 10) defined respectively by the surface bounding bore 29 and a portion of sleeve 27 and the surface defining bore 28 and a portion of sleeve 26, as shown in FIG. 10. In similar fashion, bore 39 communicates with the passages 42, 43 defined respectively by the surface bounding bore'29 and a portion of sleeve 27 and the surface defining bore 28 and a portion of sleeve 26. As shown in FIGS. 6, 8 and 10, bore 32 communicates with bores 29, 28. Particularly, bore 32 communicates with passage 44 disposed annularly of spool 27 and is annularly bounded by that spool and the surface of bore 29. Bore 32 also communicates with annular passage 45 bounded by spool 26 and bore face 28.

In similar fashion line port 33 communicates with annular passages 46, 47 respectively bounded by spool 27 and bore face 29 and spool 26 and bore face 28. Outlet port 31, as shown in FIGS. 2, 3, 5, 6, and 9, communicates with the passages 48, 49 (FIG. 10) bounded respectively by the face of bore 29 and spool 27 and the face of bore 28 and spool 26. Passage 31 also communicates with the well or vertical passage 50 (FIG. 3) downwardly through which flapper 23 extends.

Bushing 26 is secured in a predetermined position in bore 28 between end sealing plugs 51, 52 (FIG. I0) and sealingly cooperates with the surface of bore 28 between plug 51 and passage 43, between passages 43 and 45, between passages 45 and 49, between passages 49 and 47, between passages 47 and 41, and between passage 41 and plug 52. Similarly, bushing 27 is secured in a predetermined position in bore 29 between end sealing plugs 53, 54 and sealingly cooperates with the surface of bore 29 between plug 53 and passage 40, between passages 40 and 46, between passages 46 and 48, between passages 48 and 44, between passages 44 and 42, and between passage 42 and plug 54. Bushings 26, 27 have respective axial cylindrical bores 56, 57 in which valve spools 24, 25 are respectively received between the spaced end plugs 5ll-52 and 53-54 for axial movement within the range of the mechanical limits established by these end plugs. It should be noted that bore 28 and bushing 26, spool 24, end plug 51 and end plug 52 are respectively like bore 29, bushing 27, spool 25, end plug 53 and end plug 54. However, the positions of elements in bore 28 are the reverse of the position of corresponding elements in bore 29.

The bushings 26 and 27 are similar in construction. Details of construction of the bushing 26 are shown in FIG. 17. As shown, the bushing 26 includes outwardly extending ribs 261, 262, 263, 264, 266 and 267, all of which extend outwardly to form part of a common cylinder. Slots 268-268, 269-269, 271-271 and 272-272 extend through the wall of the bushing 26 to permit communication with portions of the spool thereinside.

FIGS. 11-16 are provided to show the internal fluid conducting features of the spool 24. The spool 24 has two separate fluid conducting systems; the first shown separately in FIGS. 13 and 14, the second shown separately in FIGS. 15 and 16, and both of which are shown in relation to each other in FIGS. 11 and 12. The first system has bores with axes lying in plane 13-13 in FIG. 12, which is the plane upon which FIG. 13 is taken, while the second system bores have axes lying in plane 15- 15 in FIG. 12, which is the plane upon which FIG. 15 is taken. Spool 24 has three spaced cylindrical shoulder portions 60, 62, 64 joined by smaller intermediate body portions 61, 63. The two systems have aligned bore portions 65, 66 (FIG. 19) parallel to the longitudinal axis of the spool and respectively provided in head-shoulder 60 and waist-shoulder 62.

Bore 66, part of the first system, is in communication with bore 67 which in turn is in communication with bore 68 (FIG. 13) which extends parallel to the axis of the spool from bore 67 through spool head-end face 69. As shown, particularly in FIG. 13, the portion of bore 67 extending away from bores 66 and 68 is filled by plug 67. Also, an upstream nozzle 70 is mounted in the portion of bore 66 extending from bore 67 toward tailshoulder 64 while a flapper-nozzle 71 is mounted in the portion of bore 66 extending from bore 67 toward head-shoulder 60.

Bore portion 65 in head-shoulder portion 60 is part of the second fluid conducting system in spool 24. Bore portion 65 intermediate its ends is in communication with bore 72 (FIG. which in turn is in communication with the bore 73 that extends parallel to the axis of the spool from bore 72 through spool tail-end face 74. Bore 75 provides communication from bore 73 outwardly through body portion 63. The portion of bore 65 from bore 72 to spool head-end face 69 is filled by plug 65 while the portion of bore 72 extending away from bores 65 and 73 is filled by a plug 72'. Upstreamnozzle 76 is mounted in bore 75 and flapper-nozzle 77 is mounted in the portion of bore 65 extending from bore 72 toward waist-shoulder 62.

The upstream nozzles 70, 76 have respective like metering orifices 79 and like nozzles, not shown, are also provided in corresponding spool 25. The flapper nozzles 71 and 77 (as well as corresponding flapper nozzles 81 and 82, FIG. 10, of spool 25) have like metering orifices 83, 84. The metering orifices in the flapper nozzles are preferably larger in cross-sectional area than the orifices in the upstream nozzles.

As shown in FIG. 10, the head-end face 69 of spool 24 disposed in bushing 26 in conjunction with plug 51 defines a variable head-end chamber 85 inside the bushing 26 having a volume which varies with the variation in position of the spool. Similarly, spool tail-end face 74, bushing 26, and plug 52 define a tail-end chamber 86, the volume of which also varies with axial shifting of spool 24. The volume of chamber 86 thus increases when the volume of chamber 85 decreases. Similarly, the head-end face of spool 25, together with bushing 27 and plug 53, define head-end chamber 88, and tail-end face 89 of spool 25, together with bushing 27 and end plug 54, define tail-end chamber 90. The plugs close ends of the chambers.

The spools 24 and 25 are prevented from turning out of alignment with the flapper shoe 124 (FIG. 3) by positioning pins 910 and 911 mounted in the spool 24 and similar positioning pins 912 and 913 mounted in the spool 25. The pins extend parallel to the axes of the spools and are engageable with the flapper shoe 124 to limit turning of the spools.

The positioning of spools 24, 25, in relation to the respective sleeve bushings 26, 27 is accomplished through hydromechanical cooperation between the spools and the flapper 23 of the electric torque motor 22. The correlated positioning of spools 24, 25 is accomplished by adjustment of the position of the motor 22 and its flapper 23.

In the upper portion of valve body 21 there is provided a motor chamber 100 which, as shown in FIGS. 1, 2, 3, and 4, is essentially of right cylindrical form with a frusto-conic extension 99 (FIGS. 2 and 3) of smaller diameter extending farther into the body towardbores 28, 29. From frusto-conic extension 99, well 50 extends to intersect with the bores 28, 29. Annular land face 98 is provided as a seat for a swivel mount 101. The swivel mount 10] (FIG. includes a ring-like portion 102 which rests upon the land 98 (FIGS. 2 and 3) and closely fits the cylindrical wall face 95 of the chamber outwardly adjacent the land 98 so that the swivel mount may be rotated about the axis of the cylindrical chamber 100. The swivel mount 101 (FIG. 20) also carries upwardly projecting portions 103 and 103' having V-grooves 104 and 104, respectively, in the upper extremities thereof. The center lines of the V-grooves 104, 104 coincide with thediameter through the axis of the swivel ring and the cylindrical portion of the motor chamber -99.

The motor 22 (FIG. 2) includes a body 107 provided with trunnions 108-109 (FIG. 3) which rest in the V- grooves 104-104 to pivotally support the body 107 on the swivel member 101. The ring-like portion 102 (FIG. 20) of the swivel member 101 is provided with slots 108' and 109 (FIG. 1), which are provided with radial faces 111 (FIG. 20) and 112 (FIG. 3), respectively. Transverse adjustment screws 113 and 114 (FIGS. 6 and 20) threaded in transverse bores 116 and 117 (FIG. 4), respectively, engage the radial faces 111 (FIG. 20) and 112, respectively. When one of the transverse adjustment screws 113 and 114 is retracted and the other transverse adjustment screw is advanced, the swivel member 101 is rotated for adjustment of the position thereof. Upright adjustment screws 116' and 117' (FIG. 2) threaded in bushings 118 and 119, respectively, of a cap 120 engage wing members 121 and 122, respectively, which are portions of the body 107 of the motor 22 and extend on opposite sides of the body 107 circumferentially spaced from the trunnions. The cap 120 is attached to the body or housing 21 by appropriate fasteners 120' (FIG. 1). An appropriate gasket 120" (FIGS. 2 and 3) forms a seal between the cap 120 and the body 21. Upper faces 121' and 122 of the wing members 121 and 122 are flat and extend in a plane parallel to the axis of the trunnions 108 and 109 and transversely of the radial faces 1 11 and 112 so that the body of the motor and the swivel mount 10] can turn with the upright adjustment screws engaging the upper faces. When one of the upright adjustment screws 116' and 117' (FIG. 2) is retracted and the other upright adjustment screw is advanced, the body is pivoted on the trunnions for adjustment thereof. By means of the adjustment screws, the body of the motor can be swung about the axis of the trunnions and about the axis of the body 21 to adjust a normal or null position of the flapper shoe 124 (FIGS. 3 and 10) carried by the flapper 23 so that, as shown in FIG. 10, the shoe is normally equally spaced between the flapper nozzles 71 and 77 and between the flapper nozzles 81 and 82 when the spools are aligned with each other and flow through the lines 35 and 36 is cut off. Swinging of the body 107 about the axis of the trunnions moves the null position of the flapper shoe 124 to the right or left as shown in FIG. 10 for adjusting the null position of the flapper shoe axially of the spools. Swinging of the body 107 with the swivel mount 101 turns the flapper shoe 124 about an upright axis to adjust the alignment between spools and bushings when the flapper shoe is in null position. If some center flow or leakage through the valve ports is desired to damp oscillation of a load I..carried by the piston 34', the degree of such center flow can be adjusted by swinging of the swivel mount by action of the transverse adjustment screws 113 and 114. In FIG. 10, the spools are shown in the position of critical alignment wherein the ports controlled by both spools are closed, and the ports controlled by the spool 24 will start to open as soon as the flapper shoe starts to the right and the ports controlled by the spool 25 will start to open as the flapper shoe starts to the left. The spool 24 controls movement of the piston 34 to the right and the spool 25 controls movement of the piston 34' to the left.

Operation of the servovalve of FIG. 1 can best be understood by reference to FIG. 10. As long as the flapper shoe 124 is in its centered or null position, the flapper shoe supplies equal resistance to flow through the flapper nozzles on opposite sides thereof. Fluid pressure in the passage 41 enters the bore 73 (FIG. 15) of the spool 24 through the metering orifice of the upstream nozzle 76 and enters the bore 68 (FIG. 13) through the metering orifice of the upstream nozzle 70.

Orifices of the flapper nozzles 71 and 77 (FIG. 19) are larger than the orifices of the upstream nozzles 70 and 76 (FIG. 15) so that, when the flapper shoe 124 is centered between the flapper nozzles 71 and 77, as shown in FIG. 19, equal pressures exist inside the bores 68 and 73, and there is no substantial difference in the pressures in the chambers 85 and 86 (FIG. and no resultant force tends to move the spool 24 from the position shown in FIG. 10. However, when electrical forces in the motor 22 cause the flapper shoe 124 to swing from its null position to the right as shown in FIGS. 10 and 19, the flapper shoe reduces the flow through the orifice of the flapper valve 77 causing an increase in the pressure in the bore 72 and in the bore 73 (FIG. communicating therewith to increase the pressure in the chamber 86 (FIG. 10) causing the spool 24 to move to the right as shown in FIG. 10. On the other hand, when electrical forces in the motor 22 cause the flapper shoe 124 to swing from its null position to the left as shown in FIGS. 10 and 19, the flapper shoe restricts the flow through the flapper nozzle 71 increasing the pressure inside the bore 67 and the bore 68 (FIG. 13) communicating therewith to increase the pressure in the chamber 85 (FIG. 10) causing the spool 24 to move to the left. In similar fashion, movement of the flapper shoe 124 to the right as shown in FIG. 10, causes the spool 25 to move to the right because of increase of pressure in the chamber 88 and movement of flapper shoe 124 to the left causes movement of the spool 25 to the left as pressure is increased in the chamber 89.

As already pointed out, when the spool 24 moves to the right, fluid under pressure from passage 41 reaches the line 36 through the passage 47 to supply pressure to the left hand end of the motor 34 and the hydraulic line 35 is connected to the discharge passage 49 through the passage 45. When the spool 25 is moved to the left, fluid under pressure in the passage 42 reaches the line 35 through the passage 44 to supply fluid to the right hand end of the motor 34, and the line 36 is connected to the discharge passageway 49. In the servovalve structure, the number of dimensions requiring critical spacing in each element is limited. For example, in the spool 24, the spacing between the shoulder faces 131 and 132 is the only critical spacing. The spacing between slots 133 and 134 is the critical spacing in the bushing 26, and must be equal to the spacing between the shoulder faces 131 and 132 of the spool 24.Similarly, there is but a single critical spacing in the spool 25, and there is a single critical spacing in the bushing 27.

In FIGS. 21 and 22 is illustrated a servovalve 320 constructed in accordance with another embodiment of this invention. The servovalve 320 includes a body 321 in which is mounted an electric torque input motor 322 having a flapper 323 provided with a flapper shoe 323'. The flapper shoe 323' cooperates hydromechanically with valve spools 324-325 (FIG. 28) which move inside valve sleeves or bushings 326-327. The bushings 326 and 327 are mounted in parallel bores 328 and 329, in the body 321. The servovalve body is provided with a supply or inlet port 330 (FIGS. 23 and 25) through which hydraulic fluid under pressure from a suitable source (not shown) is introduced into the body, a return or outlet port 331 (FIGS. 23 and 27) through which hydraulic fluid is discharged, and two line ports 332 (FIGS. 26 and 28) and 333, which can be coupled to a hydraulic device 334 (FIG. 28) to be operated in response to the servovalve through hydraulic lines 335, 336 to effect positioning of a piston 334' in accordance with input signals to the servovalve.

The motor 322 is provided with trunnions 338 and 339 (FIG. 22) which are supported on a swivel mount 340. Upright adjustment screws 341-342 threaded in bushings 343-344 in a cap 346 engage wing members 347-348 of the motor 322 for adjustment of the motor about the axis of the trunnions 338-339. Transverse adjustment screws 349, one of which is shown in FIG. 21, are threaded in transverse bores 351-352 (FIG. 24) and operate to swing the swivel mount 340 and the motor 322 about an upright axis in the same manner that the swivel mount of the servovalve of FIGS. 1-20 is adjusted.

As shown in FIG. 25, the valve body 321 is provided with a gallery bore 361 which places the inlet port 330 in communication with cross bores 362 and 363. The cross bores 362 and 363 intersect the parallel bores 328 and 329. Portions of the bores 361, 362, and 363 are closed by plugs 364, 366, and 367, respectively. In a similar fashion, the outlet port 331 (FIG. 27) communicates with a gallery bore 369, which, in turn, communicates with cross bores 371, 372, and 373. The cross bores 371, 372, and 373 intersect the parallel bores 328 and 329. Portions of the bores 369, 371, and 373 are closed by plugs 374, 376 and 377, respectively.

The bushings 326 and 327 (FIG. 23) are similar in construction and only the bushing 326 will be described in detail. Details of construction of the bushing 326 are shown in FIGS. 29 and 30. The bushing 326 is tubular and is provided with a central bore 381 in which the spool 324 moves. The bushing 326 (FIG. 29) is provided with outwardly extending ribs 382, 383, 384, 386, 387, 388, 389, and 391, which extend outwardly to form a common cylinder. Slots 392, 393, 394, 396 and 397 extend through the wall of the bushing 326 to permit communication with portions of the spool 324 and of outside portions of a dash-pot member 398 thereinside. The bushing 326 is mounted in the bore 328 (FIG. 28) with spaces between ribs aligned with the cross bores and the line ports of the body 321. A plug 399 closes one end of the central bore 381 of the bushing 326 with a stroke space 401 being provided inside the bore 381 between the plug 399 and the spool 324.

Details of construction of the spool 324 are shown in FIGS. 31 and 32, the other spool and associated members being of similar construction but oppositely oriented. The spool 324 includes ribs 402, 403, and 404 which fall in a common cylinder. Lengthwise bores 406 and 407 extend parallel to the axis of the spool. The bore 406 communicates through a cross bore 408 with the space between the ribs 402 and 403 through which fluid under pressure is introduced into the bore 406.

The bore 407 opens through an end face or wall 411 of the spool. The bore 406 is closed at one end at the end wall 411 by a plug 412. The other end of the bore 406 terminates in an orifice 413 which discharges through an opening inan end face or wall 414 of the spool into a dash-pot well 416 in the dash-pot member 398. Fluid under pressure from the bore 406 enters the bore 407 through an upstream orifice 417 (FIG. 33). The bore 407 is connected to a flapper nozzle 418 by channel bores 4'19 and 421 in the spool so that fluid is discharged from the bore 407 through the channels 419 and 421 and a flapper nozzle orifice 4210 (FIG. 33) against the flapper shoe 323'. The flapper nozzle orifice 4210 is of greater diameter than the upstream orifice 417 so that the pressure in' the bore 407 is less than that in the bore 406. A plug 4211 closes a portion of the bore 419'. The flapper nozzle 418 is mounted in a counterbore portion 4212of the bore 421. The spool is provided with guide pins 4213 and 4214 (FIG. 22) which are engageable with the flapper shoe 323' to prevent rotation of the spool.

The dash-pot member 398 includes a head 422 (FIG. 31) which fits inside the bore 328 (FIG. 28) and against an end of the bushing 326.'A shank 423 (FIG. 31) of the dash-pot member 398 extends inside the central bore 381 of the bushing 326, as shown in FIG. 28. An O-ring 424, which is received in an annular slot 426 (FIG. 31) of the dash-pot member 398, forms a seal between the dash-pot member 398 and the bushing 326. A lengthwise slot 427 in the shank of the member 398 permits fluid which escapes from the well 416 to be discharged through an annular slot 428 in the shank 423. A threaded socket 429 is provided in the member 398 for insertion of an appropriate tool (not shown) for withdrawing the member 398 from the bore 328. A ring 431 (FIGS. 28 and 34), threaded in the end portion of the bore 328, positions the member 398 in the bore 328. A central hexagonal opening 432 is provided in the ring 431 for insertion of an appropriate tool (not shown).

As shown in FIG. 31, the diameter of the end wall 411 of the spool 324 is greater than the diameter of the opposite end wall 414, and preferably the area of the end wall 411 is twice that of the end wall 414.

Operation of the servovalve of FIGS. 21-33 can best be described by reference to FIG. 28. As already pointed out, the source of fluid under pressure is connected to the supply or inlet port 330 (FIG. 25) and via the gallery port 361 to the cross bores 362 and 363. The cross bore 362, in turn, communicates with an annular space 433 (FIG. 28) between the ribs 383 and 384 of the bushing 326, and the cross bore 363 (FIG. 25) communicates with an annular space 434 between the ribs 388 and 389 of the bushing 326. Annular spaces 436 437 and 438 between bushing ribs similarly communicate with the cross bores 371, 372, and 373 (FIG. 27), respectively, and therethrough with the discharge port 331. An annular space 4381 between the ribs 384 and 386 communicates with the line port 332 and an annular space 4382 between the ribs 387 and 388 communicates with the line port 333. Fluid under pressure in the annular space 433 (FIG. 28) enters a space 439 between the ribs 402 and 403 (FIG. 31) of the spool 324 and passes through the bore 408 to provide fluid under pressure in the bore 406.

The fluid under pressure in the bore 406 exerts pressure through the orifice 413 (FIG. 33) in the dash-pot well 416 which urges the spool 324 to the left as shown in FIGS. 31 and 28. Fluid from the line 406 flows through the upstream orifice 417 into the bore 407 and out through the channel bores 419 and 421 to be discharged through the flapper nozzle 418 into a space 441 (FIG. 28) surrounding the flapper shoe 323, which space 441 communicates through the annular space 437 and the cross bore 372 (FIG. 27) with the discharge port 331. As shown in FIG. 33, the flapper nozzle 418 is directed toward the flapper shoe 323, and the flapper shoe 323 restricts flow through the flapper nozzle 4210 so that the pressure inside the bore 407 is determined by the spacing between the flapper shoe 323' and the flapper nozzle 418, and the pressure inside the bore 407 is less than that inside the bore 406. The pressure inside the bore 407 is exerted through the wall 411 (FIG. 31) into the stroke space 401 (FIG. 28) urging the spool 324 to the right. The pressure inside the bore 406 is exerted through the orifice 413 into the well 416 and against the end wall 414. The pressure in thebore 406 is greater than the pressure inside the bore 407 but the area of the wall face 411 exposed to the pressure inside the bore 407 is greater than the area of the wall face 414 exposed to the pressure inside the bore 406, and the forces tending to move the spool are balanced when the spacing between the flapper shoe 323' and the flapper nozzle 418 is a selected distance.

When the flapper shoe 323' is moved to the leftas shown in FIGS. 28 and 31, the pressure inside the bore 407 is reduced so that the spool 324 is moved to the left. When the flapper shoe 323' is moved to the right,

the pressure inside the bore 407 is increased and the spool 324 moves to the right.

The restriction in the orifice 413 serves to restrict flow of fluid therethrough during movement of the spool 324 to reduce or prevent fluttering or oscillation of the spool and also to raise the hydraulic natural frequency of the spool by the formation of a trapped oil spring in the dash-pot well. This trapped oil spring in the dash-pot well supplements a second trapped oil spring in the stroke space 401.

The diameter of the orifice 413 is sufficiently great to permit oil flow therethrough so that the spool can move as required, but the diameter is sufficiently small to provide a damping of oscillatory movement. In a typical valve construction where the diameter of the upstream orifice is 0.007 inch, the dash-pot orifice 413 should be approximately 0.003 to 0.026 inch. Such dimensions are suitable for a servovalve having a rated capacity of 5 gallons per minute and provided with bores 406 and 407 of a diameter of approximately onesixteenth inch. Thus, the diameter of the dash-pot orifice is of the same order as the diameter of the upstream orifice. If the other dimensions of the servovalve are varied, the dash-pot orifice diameter can be varied accordingly. When the spool 324 is moved to the right as shown in FIG. 28, communication is provided between the annular space 433 and the annular space 4381 to put pressure in the line port 332,'and communication is also provided between the annular space 437 and the annular space 4382 to connect the line port 333 to the discharge port 331, and the piston 334' is caused to move to the right until such time as the flapper shoe 323 is returned to the normal or null position shown in FIG. 28 and the spool 324 returns to the FIG. 28 position.

In a similar manner, when the flapper shoe 323 is moved to the left from the position of FIG. 28, the spool 325 moves to the left to provide communication between annular spaces 451 and 452 of the bushing 327 to connect the line port 332 to the discharge port 331 (FIG. 27). The discharge port 331 communicates with the space 452 (FIG. 28) and with the space 441 surrounding the flapper shoe, as already pointed out. At the same time, communication is provided between annular spaces 453 and 454 (FIG. 28) of the bushing 327 to connect the line port 333 to the pressure port 330 (FIG. 25), and the piston 334' (FIG. 28) is moved to the left until such time as the flapper shoe 323' (FIG. 28) is returned to its normal or null position shown in FIG. 28. The null and center flow positions of the flapper shoe 323 and hence of the spools 324 and 325 relative to the bushings 326 and 327 are adjustable by means of the upright adjustment screws 341 and 342 (FIG. 21) and the transverse adjustment screws 349 in the manner already described with relation to the first embodiment. The null position is adjustable so that flow through the lines 335 and 336 is cut off when the flapper shoe 323 is at its null position with respect to the torque motor. The amount of center flow may be adjusted from open center down to critical center by adjustment of the transverse adjustment screws 349 to provide the precise degree of damping required by a load 474 (FIG. 28) which is attached to the piston 334'.

In the device of FIGS. 21-34, as in the device of the other Figures, there is but a single critical spacing on each spool and on each bushing. The spacing between slot faces 471 (FIG. 29) and 472 of the bushing 326 must be equal to the spacing between shoulder faces 473 (FIG. 31) and 474 of the spool 324, but this is the only spacing requiring critical forming on these parts. Similarly, there is only a single critical spacing on the bushing 327 (FIG. 28) and the spool 325.

The servovalve structures illustrated in the drawings and described above are subject to structural modification without departing from the spirit and scope of the appended claims.

Having described my invention, what I claim as new and desire to secure by letters patent is:

1. A servomechanism which includes a casing, a swivel mount, means mounting said swivel mount on said casing for swinging about an axis, a first motor having a housing, means mounting said first motor on the swivel mount for rotation about an axis extending transversely of the axis of swinging of the swivel mount, a flapper arm driven by the first motor and swinging about the axis of swinging of the motor housing, a pair of valve spool members mounted in the casing for movement transversely of the axis of swinging of the flapper arm, each of said spool members including a pair of flapper nozzles, the flapper nozzles being directed toward opposite sides of the flapper arm, means for directing fluid under pressure through the flapper nozzles, and means for moving the spool member in a direction to equalize the spacing between flapper nozzles and the flapper arm when the flapper arm is moved toward one of the pair of flapper nozzles, ports operated by the spoolmembers to introduce fluid under pressure from a source of fluid under pressure into a hydraulic actuator when the spool members move from a null position to a displaced position to operate the hydraulic actuator, the pairs of flapper nozzles of the spools being spaced from each other, means for swinging the motor housing about the axis of swinging thereof, and means for swinging the swivel mount inside the casing for moving the flapper arm to a position where the spool members are in the null positions thereof when the flapper arm is in a null position.

2. A servomechanism as in claim 1 wherein one of said spool members controls ports for supplying fluid to the hydraulic actuator for movement in one direction and the other of said spool members controls ports for supplying fluid to the hydraulic actuator for movement in an opposite direction.

3. A servomechanism as in claim 1 wherein each of the spool members is slidably mounted in a slideway having closed ends and each flapper nozzle of the spool member is connected to a channel in the spool member which extends to the end of the spool member faced by the flapper nozzle so that when pressure increases inside the flapper nozzle as the flapper arm is moved toward the flapper nozzle, pressure is increased at the end of the spool member faced by the flapper nozzle to move the spool member in a direction to move the flapper nozzle away from the flapper arm.

4. A servomechanism which comprises a casing, a swivel mount, means mounting said swivel mount on said casing for swinging about an axis, a first motor having a housing, means mounting said first motor on the swivel mount for rotation about an axis extending transversely of the axis of swinging of the swivel mount, a flapper arm driven by the first motor and swinging about the axis of swinging of the motor housing, a pair of transverse passageways in the casing, an upright well in the casing intersecting the transverse passageways, the flapper arm swinging in the upright well, a sleeve bushing mounted in each of the transverse passageways, each of the sleeve bushings including a plurality of outwardly extending sealing ring portions sealingly engaging the wall of the passageway in which the bushing is mounted, the bushing having a plurality of ports through the wall thereof intermediate the sealing ring portions, the ports including a pressure port, a return port, a first hydraulic output port and a second hydrau lic output port, plug members in the passageways at opposite ends of the sleeve bushings closing ends of the bushings, a valve spool member mounted in each bushing for movement therealong, each spool member including end shoulder portions at opposite ends thereof and an intermediate shoulder portion spaced from the end shoulder portions, there being portions of reduced diameter between the shoulder portions, two of the shoulder portions closing the hydraulic output ports in the bushing associated therewith when the spool member is in a null position, one of the hydraulic output ports being open to communicate with the pressure port and the other of the hydraulic output ports being open to communicate with the return port when the spool member is in a displaced position, each of said spool members including a pair of flapper noules; the nozzles, nozzles being directed toward opposite sides of the flapper arm, there being ports in the spool member connecting the pressure port with the flapper nozzles so that fluid under pressure from the pressure port can flow through the flapper nozzles, there being channels in the spool member extending from each flapper nozzle to the end of the spool member faced by the flapper nozzle so that when pressure inside the flapper nozzle increases as the flapper arm is moved toward the flapper nozzle, pressure is increased at the end of the spool member faced by the flapper nozzle to move the spool member in a direction to move the flapper nozzle away from the flapper arm, the spool member moving in'a direction to equalize the spacing between flapper nozzles and the flapper arm, the hydraulic output ports being connectable to a hydraulic actuator whereby fluid under pressure is delivered to the hydraulic actuator when the spool members are displaced from the null position, means for swinging the motor housing about the axis of swinging thereof and means for swinging the swivel mount inside the casing for moving the flapper arm to a position where the spool members are in the null positions thereof when the flapper arm is in a null position.

5. A servomechanism as in claim 4 wherein hydraulic output ports of one of the bushings are connected for driving the hydraulic actuatorin one direction and the hydraulic output ports of the other bushing are connected for driving the hydraulic actuator in an opposite direction.

6. In a servomechanism which includes an input motor which drives a flapper arm and a hydraulically driven output motor, valving mechanism for directing fluid under pressure to the output motor which comprises a housing, there being a pair of parallel slideways in the housing, a spool valve member slidably mounted in each slideway, port means for supplying fluid under pressure to each slideway, port means for exhausting fluid connected to each slideway, port means connecting each slideway to one side of the output motor, port means connecting each slideway to an opposite side of the output motor, valving means on each spool valve member for closing the port means associated therewith when the spool valve member is in a' closed position, movement of one of the spool valve members in one direction connecting the ports associated therewith for driving the output motor in one direction, movement of the other spool valve member in an opposite direction connecting the ports associated therewith for driving the output motor in an opposite direction, fluid operated nozzle means in each of the spool valve members arranged to cause the spool valve members to follow the flapper arm, means for supporting the input motor in the housing for rotation about a first axis and means mounting said input motor for rotation about an axis transverse to said first axis, and first and second means for advancing the input motor about said first and transverse axes, respectively, to position the flapper arm with the spool valve members in closed position when the input motor is in a null position, operation of the input motor to move the flapper arm in one direction causing the spool valve members to move therewith for supplying fluid to the'output motor for driving the output motor in one direction, operation of the'input'motor to move the flapper arm in the opposite direction causing the spool valve members to move therewith for supplying fluid to the output motor for driving the output motor in the opposite direction.

7. A servomechanism as in claim 6 wherein the input motor is an electric powered torque motor.

8. Aservomechanism as in claim 6 wherein the fluid operated nozzle means in each spool valve member includes a pair of flapper nozzles mounted in the spool valve member and directed toward the flapper arm in opposite directions and on opposite sides of the flapper arm, channels in the spool valve member connecting each flapper nozzle toan opening'in an end wall of the spool valvemember faced by the flapper nozzle, means for introducing fluid under pressure into each channel, a restricted passageway in each of the fluid introducing means, and means for closing the slideway associated with the spool valve member at opposite ends ofthe spool valve member, whereby, when pressure inside one of the flapper nozzles increases as the flapper arm is moved toward said one of the flapper nozzles, pressure in a channel associated therewith causes increase in pressure in a chamber inside the slideway at the end of the spool valve member faced by said one of the flapper nozzles to cause the spool valve member to move to follow the flapper arm.

9. A servomechanism as in claim 1 wherein the ports operated by each valve spool member are disposed in a sleeve bushing surrounding the valve spool member.

10. A servomechanism as in claim 6 wherein there is a sleeve bushing inside each slideway surrounding the spool valve member thereof and the valving means on the spool valve member cooperates with slot means in the bushing for closing the port means.

11. In a servomechanism which includes an input motor which drives a flapper arm and a hydraulically driven output motor, valving mechanism for directing fluid under pressure to the output motor which comprises a housing, there being a pair of parallel slideways in the housing, a spool valve member slidably mounted in each slideway, port means for supplying fluid under pressure to each slideway, port means for exhausting fluid connected to each slideway, port means connecting each slideway to one side of the output motor, port means connecting each slideway to an opposite side of the output motor, valving means on each spool valve member for closing the port means associated therewith when the spool valve member is in a closed position, movement of one of the spool valve members in one direction connecting the ports associated therewith for driving the output motor in one direction, movement of the other spool valve member in an opposite direction connecting the ports associated therewith for driving the output motor in an opposite direction, fluid operated nozzle means in each of the spool valve members arranged to cause the spool valve members to follow the flapper arm, means for supporting the input motor in the housing for rotation about an axis substantially aligned with the flapper arm and means for rotating the motor supporting means for aligning the spool valve members when the input motor is in a null position, operation of the input motor to move the flapper arm in one direction causing the spool valve members to move therewith for supplying fluid to the output motor for driving the output motor in one direction, operation of the input motor to move the flapper arm in the opposite direction causing the spool valve members to move therewith for supplying fluid to the output motor for driving the output motor in the opposite direction.

12. A servomechanism as in claim 11 wherein the fluid operated nozzle means in each spool member includes a pair of channels in the spool member, means connecting one of the channels to the port means for supplying fluid under pressure, an upstream orifice connecting said one of the channels to the other channel, the spool member having opposite end faces exposed to enclosed spaces, one of the end faces being of larger area than the other end face, said one of the channels communicating with the enclosed space at the smaller end face, the other channel communicating with the enclosed space at the larger end face, and a nozzle communicating with the other channel and directed toward a side of the flapper arm facing the smaller end face of the spool, the flapper arm normally restricting flow through the flapper nozzle, whereby a sufficient pressure is maintained in the other channel of the spool member to cause the spool member to remain stationary when the flapper arm is a predetermined distance from the flapper nozzle.

13. In a servomechanism, a spool valve member having a body which includes a pair of channels, means connecting one of the channels to a pressure supply port for supplying fluid under pressure to said one of the channels, an upstream orifice connecting said one of the channels to the other channel, the spool member having opposite end faces exposed in enclosed spaces, one of the end faces being of larger area than the other end face, said one of the channels communicating with the enclosed space at the smaller end face, the other channel communicating with the enclosed space at the larger end face, and a nozzle communicating with the other channel and directed toward a side of a flapper arm facing the smaller end face of the spool, the flapper arm normally restricting flow through the flapper nozzle, whereby a sufficient pressure is maintained in the other channel of the spool member to cause the spool member to remain stationary when the flapper arm is a predetermined distance from the flapper nozzle, the fluid pressure causing the spool valve member to move to follow the flapper arm when the flapper arm is moved, and line port means controlled by the spool valve member.

14. A servomechanism as in claim 13 wherein the area of the larger end face is substantially twice the area of the smaller end face.

15. A servomechanism as in claim 13 wherein the communication between said one of the channels and the enclosed space at the smaller end face is restricted to damp oscillatory movement of the spool.

16. In a servomechanism, a pair of spool valve members, each of said spool valve members having a body which includes a pair of channels, means connecting one of the channels to a pressure supply port for supplying fluid under pressure to said one of the channels, an upstream orifice connecting said one of the channels to the other channel, each of the spool valve members having opposite end faces exposed in enclosed spaces, one of the end faces beingof larger area than the other end face, said one of the channels communicating with the enclosed space at the smaller end face, the other channel communicating with the enclosed space at the larger end face, and a nozzle communicating with the other channel, means for mounting the spool valve members for sliding parallel to each other, a flapper arm, the larger end of one spool valve member being opposed to the large end of the other spool valve member, the nozzles of the spool valve members being directed toward opposite sides of the flapper arm, each nozzle facing the smaller end face of the associated spool valve member, the flapper arm normally restricting flow through the flapper nozzles, whereby a sufficient pressure is maintained in the other channel of each of the spool valve members to cause the spool valve members to remain stationary when the flapper arm is a predetermined distance from the flapper nozzles, the fluid pressure causing the spool valve members to move to follow the flapper arm when the flapper arm is moved, and line port means controlled by each of the spool valve members.

UNITED STATES PATENT OFFICE QERTIFIC ATE OF DORRECTI-ON Patent 3,759,145 Dated September 18 1973 Inventor(s) WILLIAM w. TAYLOR It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 12, line 58, (semicolon) should be (comma) Column 12, line 59, "nozzles," (first occurrence) should be flapper Signed and sealed this25th day of December 1973.

(SEAL) Attest:

EDWARD M.Fl.ETCI-]IEE, JR. RENE D. TEGTl IEYER Attesting Officer Acting Commissioner of Patents Q USCOMM-DC 60376-P69 U,S. GOVERNMENT PRINTING OFFKCE: I969 O366-334 

